Ch 4: Fluid and Electrolytes, Acids and Bases
total body water (TBW)
sum of fluids in all body compartments. about 60% body weight. one liter weighs about one kg.
capillary hydrostatic pressure (BP)
outward movement of water fom the capillary to interstitial space
capillary oncotic pressure
osmotically attracts water from interstitial space back into capillary
Interstitial hydrostatic pressure
inward movement of water from interstitial space into capillary
interstitial oncotic pressure
osmotically attracts water from capillary into interstitial space
net filtration=(forces favoring filtration)-(forces opposing filtration)
forces favoring filtration: capillary hydrostatic pressure and interstitial oncotic pressure
forces opposing filtration: capillary oncotic pressure and Interstitial hydrostatic pressure
water movement between ICF and ECF
water moves freely by diffusion through lipid bilayer cell membrane and through aquaporins
ICF is not subject to change in osmolality, but when ECF osmolality changes, water moves from one compartment to another until equilibrium is reached
excessive accumulation of fluid within interstitial spaces
increase capillary hydrostatic pressure, decreased plasma oncotic pressure, increased capillary membrane permeability, and lymphatic channel obstruction
increases with venous obstruction or salt and water retenton
caused by thrombophlebitis, hepatic obstruction, tight clothing around extremities, prolonged standing
salt and water retention
CHF, renal failure, and cirrhosis
decreased oncotic pressure
result of low or diminished plasma albumin production.
causes: plasma proteins are lost in glomerular diseases of the kidney, serous drainage from open wounds, hemorrhage, burns, and cirrhosis
results in edema
increases with inflammation and immune responses
proteins escape and produce decreased capillary oncotic pressure which causes edema
fluids and proteins accumulate in interstitial fluid.
occurs when lymphatic channels are blocked or removed.
fluid accumulates in gravity-dependent areas
characterized by pitting edema
secretion influenced by circulating blood volume and blood presuure and plasma conc of sodium and potassium
promotes renal sodium and water reabsorption and excretion of potassium, increasing blood vol. vasoconstriction elevates the systemic blood pressure and restores renal perfusion (blood flow). renin release is inhibited once balance is restored
antidiuretic hormone (ADH)
regulates water balance
makes up 90% of ECF cations
along with consituent anions (chloride and bicarbonate) regulates water balance
neuromuscular irritability for nerve impulses, regulation of acid-base balance, participation in cellular chemical reactions and transport of substances across the membrane
released when blood vol or BP is reduced
stimulates formation of angiotensin I
Angiotensin converting enzyme (ACE)
in pulmonary vessels converts angiotensin I to angiotensin II which stimulates secretion of aldosterone,and also causes vasoconstriction
released when there is an increase in mean arterial pressure.
natural antagonists to RAA system
cause vasodilation and increase sodium and water excretion, decreasing BP
major anion in ECF, and provides electroneutrality in relation to sodium
transport is passive to active sodium transport
regulated by secretion of ADH/vasopressin
secreted when plasma osmolality increases or circulating blood volume decreases and blood pressure drops
stimulated by increased osmolality
causes thirst and signals the pituitary to release ADH which increases water reabsorption into plasma
volume-sensitive receptors and baroreceptors
nerve endings sensitive to changes in volume and pressure
stimulates release of ADH from pituitary glad and stimulate thirst and signals release of ADH
VSR's located in atria and thoracic vessels, baroreceptors in the aorta, pulm arteries and carotid sinus
ADH secretion also occurs when atrial pressure drops, as occurs with decreased blood vol
isotonic fluid loss
fluid vol decreases but conc of solutes remain the same
results from hemorrhage, severe wound drainage, excessive sweating and inadequate fluid intake
isotonic fluid excess
results from excessive administration of intravenous fluids, hypersecretion of aldosterone, or drugs like cortisone (causes renal reabsorption or sodium and water)
serum sodium levels exceed 145 mEq/L
may cause hypervolemia, water loss ICF and ECF dehydration occurs
commonly results from oversecretion of aldosterone or adrenocorticotropic hormone
often accompanied by hyperchloremia
clincal manifestations: increased BP, bounding pulse, and weight gain
treatment, give oral fluids until serum sodium levels return to normal
leads to intracellular overhydration and cell swelling
results from sodium deficit. osmotic pressure of ECF decreases and water moves into cell where osmotic pressure is greater. plasma volume decreases
also results from water exccess
serum sodium conc falls below 135 mEq/L
causes hypoosmolality with movement of water into cells
dilutional hyponatremia occurs with fluid replacement with 5% dextrose
decrease in cellular ability to depolarize and repolarize efficiently. lethargy, depressed reflexes, seizures
occurs with CF, hyponatremia, or elevated bicarbonate conc
results from acute renal failure, severe CHF, and cirrhosis, syndrom of innappropriate secretion of ADH(SIADH)
dilution of ECF
predominant ICF ion, major influence on osmolality and fluid balance
required for glycogen and glucose deposition in liver and skeltal muscles, maintains resting membrane potential, cardiac rhythms, and smooth and skeletal muscle contraction
lowered serum potassium level, loss of total body potassium
K+ shift from ICF to ECF can cause diabetic ketoacidosis, increased H+ ion in ECF causes H+ to shift into the cell in exchange for K+. it is lost in the urine causing deficit in total body K+.
loss of fluid and sodium stimulates secretion of aldosterone which can cause renal losses of K+
mild losses of potassium are asymptomatic. severe losses cause neuromuscular excitability, muscle weakness, cardiac dysrythymias, etc
H+ ion must be regulated to maintain membrane integrity and speed of metabolic enzymes
lungs kidneys and bones are responsible for regulation
two forms, volatile (can be eliminated as CO2 gas) and nonvolatile (can be eliminated by the kidney
volatile is carbonic acid H2CO3, a weak acidthat does not release H+ easily. carbonic anhydrase splits it into CO2 and H2O. it is released in exhalation
nonvolatileare other organic gases like sulfuric, phosphoric. secreted into urine
buffers absorb excess H+ or hydroxyl OH- and prevent change in pH.
most important plasma buffers are carbonic acid-bicarbonate and protein hemoglobin.
ammonia and phosphate are important renal buffers
carbonic acid-bicarbonate buffer.
lung and kidney.
lungs blow out CO2 leaving H2O.
kidneys reabsorb bicarbonate or regenerate new bicarbonate from CO2 and water.
respiratory system compensates for changes in pH by increasing or decreasing CO2 levels by ventilation
"correction occurs" when balance is achieved.